Being that your son is in the Air Force, it is very easy to have a custom knife made in the USA shipped to his APO address in Japan.
I would have your son contact Randall Made Knives. Randall's are one of the few knifes that are still hand forged. Randalls have about a 5 year waiting period, Unless you are active duty military serving overseas, then there is about a 8 week waiting period!!! Randall has a very rich history with US Military personnel and still support them, and can still get them for around $300 or so, which is a excellent price considering the value, quality and sheath that comes with a Randall. I was overseas with the military in 2003 and ordered a Randall and got it in less than 2 weeks!! They even customized it with some modifications I asked for. Great service.
http://www.randallknives.com/
There are some other really good custom makers as well. Check out Ryan Wilson, at
http://www.wilsontactical.com/knives.aspx He will also modify and make a knife to your specs and does great work.
If your son get a chance to do any travel throughout Asia while he is in Japan, tell him to head on over to Cambodia. Good custom knife shop based out of Phnom Penh. Citadel knives. Ran by a couple of French guys and they make excellent and good quality knives at very good prices if buy in Cambodia (most are under $100, but they sell them in Europe for around 3-4x that). THey also produce and custom make some of the nicest Japanese Katana Swords I have ever seen. Using all traditional techniques. They will sell in Cambodia for around $600 - $1500, but again they are being sold in Europe for 3-4x that amount. For the price of what a custom katana will run in Japan, your son could fly to Cambodia, spend a week in a 5 star hotel, eat at 5 star restuarants, see the sights, buy a Custom Katana and still have money left over in his pocket!
Also, if your son wants a real great semi-custom made folder, check out the Sebenzas by Chris Reeve. Can get them with various wood inlays or graphics, and they will even put a custom graphic or engraving on the handle for you.
http://www.chrisreeve.com/sebenza.htm CRK also offers a good discount for Military personnel serving overseas, and Chris Reeve is a big supporter of the US Military. His fixed bladed one peice knives are also great quality and very tough.
Cheers!